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108 Professor J. A. Fleming [March 27, 



The G.P.O. are now also laying an underground air-space paper 

 coil-loaded cable 3 in. in diameter containing fifty circuits, between 

 London and Liverpool via Birmingham, a total distance of 200 miles. 

 Mr. Siingo informs me this cable contains the following loops : — 



2 circuits of 800 lb. per mile. 1 



14 circuits of 200 lb. per mile. * 



12 circuits of 150 lb. per mile. 

 24 circuits of 100 lb. per mile. 



These circuits are double metallic circuits arranged as multiple- 

 twin circuits in a lead sheath. The wire-to-wire capacity of all 

 loops is 0*065 microfarad per mile. These cables are all loaded with 

 coils spaced 2*5 miles apart, and the added inductance is 0*055 

 henrys per mile of loop. The ratio S/C is 20. The thicker wires 

 have coils of lower resistance than the thinner wires. This cable, 

 when completed, will afford improved telephonic communication 

 between London, Birmingham, and Liverpool, which will be quite 

 independent of storm or weather. 



In the United States a still longer coil loaded telephone cable 

 has been laid between Boston and Washington, passing through 

 New York, Philadelphia, and Baltimore, a total of 475 miles. This 

 cable is a multiple cable, and includes seven circuits of No. 10 wires, 

 which can be phantomized in pairs. The Pupin coils are inserted 

 every 1*4 mile. The phantom circuits between New York and 

 Washington have a transmission efficiency equal to thirteen miles of 

 standard cable, and between Boston and Washington equal to twenty- 

 six miles. 



Up to 1912 in the United States, telephone circuits of a total 

 length of 103,000 miles had been equipped with loading coils, and a 

 great improvement effected in the range and transmission efficiency. 



To sum up : we can say from an inspection of the figures given 

 above that it is now possible by suitably loading a telephone line to 

 increase its telephonic range two or three times. The chief diffi- 

 culty which is encountered in the loading of aerial lines is the 

 variable leakance over the insulators, which may under some condi- 

 tions reduce the effect of loading to nil. Broadly speaking, however, 

 the introduction of loading has made possible telephony by overhead 

 lines to a distance of 2000 miles, and this may, perhaps, in the near 

 future be increased to 3000 miles. It has rendered possible com- 

 mercial telephony by underground cables up to a distance of about 

 400 miles, and this may be increased to 500 miles before long. It 

 has enabled submarine telephone cables to be laid for distances of 

 sixty to seventy miles, and it is within possibility to increase this to 

 150, or perhaps 200 miles. 



We may ask in conclusion what prospect exists of abolishing the 

 line altogether, with its troublesome attenuation and distortion of 

 wave form. 



